The invention disclosed and claimed herein generally pertains to improved apparatus for supporting or mounting the respective coils of a gradient coil assembly within the bore of the main magnet of a magnetic resonance (MR) imaging system. More particularly, the invention pertains to apparatus of the above type which provides very effective vibration isolation, that is, which substantially prevents transfer of mechanical vibrations from the MR gradient coil assembly to the main magnet and to structures adjacent thereto. Even more particularly, the invention pertains to apparatus of the above type which is comparatively simple and inexpensive, and which achieves its purposes without degrading image quality, and without adding limitations to current transportation and handling procedures.
As is well known by those of skill in the art, an MR scanner or imaging system requires gradient coils to generate the X-, Y-, and Z-gradient fields required for imaging. In a common arrangement, each gradient field is produced by a pair or set of gradient coils, wherein each coil is wrapped around one of two cylindrical coil forms. The two coil forms are placed in coaxial relationship, and the coil forms and respective X-, Y- and Z-gradient coils collectively comprise a gradient coil assembly. Arrangements of this type are described, for example, in U.S. Pat. No. 5,570,021, issued Oct. 29, 1996 and commonly assigned herewith to the General Electric Company. Two of the inventors named in such patent are coinventors herein. Such arrangements are also described in U.S. Pat. No. 5,760,584, issued Jun. 2, 1998 and likewise assigned to the General Electric Company. Typically, the gradient coil assembly must be mechanically supported within the cylindrical bore of a static or main magnet, which is another essential component for an MR imaging system.
As is further well known, respective gradient coils of an MR system are electrically excited to impose time varying magnetic fields on the primary or static magnetic field, which is produced by the main magnet. When a gradient coil is subjected to such excitation, the coil tends to be mechanically displaced or vibrated. Frequently, the mechanical structure used to support the gradient coil assembly within the main magnet bore provides a path for transferring or coupling the vibrations of the gradient coils to the main magnet structure. Generally, the main magnet is supported on the floor of the building in which the MR system is operated. Accordingly, the gradient generated vibrations may be directly coupled from the magnet to the floor, and then travel therethrough to vibrate structures throughout the building. As a result, gradient coil vibrations can couple acoustically to rooms outside of the MR scan room, i.e., a room which is specially constructed to house the MR system.
It will be readily apparent that the transmission of gradient coil vibrations through building structure is particularly undesirable when the MR system is used in a hospital or other health care facility. Moreover, the recent introduction of shorter and lighter high field magnets now allows users to install MR systems in areas of hospitals and clinics that are located close to occupied rooms, such as patient rooms and doctor examination rooms. This development has made the transfer of gradient coil-induced noise even more objectionable. Such noise may appear to be nearly as great in rooms which are proximate to the MR scan room as it is within the scan room itself. However, past efforts to reduce vibrations generated by MR gradient coils have been, at best, only partially successful. A gradient coil must be mechanically stable, with respect to the main magnet, during the imaging sequence. Otherwise, image quality may be reduced or degraded. Also, it is very desirable to have the gradient coils physically connected to the main magnet for transportation purposes. This provides the ability to transport the magnet to a site of use without any need for shipping constraints, which would otherwise need to be removed upon arrival at the site.